70 GODFREY SYKES 



them. This configuration lends itself to a system of irrigation 

 by submersion and so it has happened that at a very early period 

 the land was watered and fertilized by a simple cutting of the 

 bank and subsequent control of the outpouring water, during the 

 season of highest river and' maximum silt content. 



In order to render this annual flooding more certain and safe, 

 the irrigable areas were soon traversed by a reticulation of earthen 

 dikes or barriers, and many of these, slightly modified from time 

 to time to suit the growth or decline of various communities, are 

 doubtless still in use today. 



The method of iiTigation is substantially as follows: The 

 river gates are opened to admit the rising Nile about the middle 

 of August, and the water is allowed to fill the basins between the 

 various dikes to an average depth of about 5 feet, and remain upon 

 the land for a period of forty days. The silt has settled during 

 this time and the clear water is then allowed to return to the 

 river, or, if it is a season of comparatively low Nile, it is used to 

 flood other basins further down the valley. 



This system of submersive irrigation possesses the merit of 

 feeding as well as watering the thirsty soil, for at the time of the 

 admission of the water, the annual silt-laden flood from the 

 Atbara, the lowest of the Nile's tributary streams, is supplement- 

 ing the clearer water of the Nile itself. 



The disadvantage of the system lies in the fact that even in 

 this land of perpetual sunshine and perennial plant growth, it onl}' 

 provides for one cropping per j^ear, and so a dependence upon sub- 

 mersi\'e ii-rigation alone would soon have failed to provide for the 

 dense population which thronged the \'alley of Egypt even under 

 the Pharaohs. The construction of canals in conjunction with 

 temporary' and partial barrages in the ri\'er, designed for the pur- 

 pose of getting water upon the land at other times of the yesLr, was 

 undoubtedly begun at a very early period, and thus the purely 

 submersive system was supplemented by the perennial method of 

 U'rigation. The available resources of the ancient Egyptians 

 perhaps hardly enabled them to cope successfully with a complete 

 damming and control of their great river, although this is the 

 line along which modern engineering effort has been chief!}' di- 



